This invention relates to a method for coating cathode material onto a cathode substrate for a vacuum electron tube, and particularly for a cathode-ray tube.
A cathode-ray tube includes at least one electron gun, which is a means for producing a highly collimated electron beam. The usual electron gun includes a cathode comprising a cathode substrate carrying a thin layer of electron-emissive material, and at least one grid having a beam-forming aperture therein closely spaced a precise, predetermined distance from the electron-emissive layer. In one design, the layer is smaller than, and concentric with, the beam-forming aperture in order to improve the collimation of the beam.
This one design has been assembled by prior methods of assembly in which the cathode coating is produced on the cathode substrate, one or more grids are fixedly assembled in a mount assembly, and then the coated cathode substrate is fixedly assembled in the mount assembly. Subsequently, the cathode coating is converted to an electron-emissive layer. With the prior methods of assembly, it has proven difficult to assemble the cathode coating concentrically with the grid aperture with the desired accuracy and precision. This deficiency in concentricity with the grid aperture occurs even when the cathode coating is produced on the cathode substrate by punching the cathode coating from a foil and transferring it directly onto the cathode substrate in the punching mechanism, as described, for example, in U.S. Pat. No. 3,282,762 to F. Stork et al.